I sell a lot of old clothing (...and buy a lot too). Last week I finished a big purge and made $275 for my trouble, which was enough to make me feel a little less bad about the revolving door of my wardrobe.
I sell mostly to local trendy second-hand stores. Crossroads and Buffalo Exchange are chains (mostly local to SF) that buy recent, mid-range clothing, things you could buy now. They're picky: they want things they know will sell well, and no fast fashion. Their customer base is trendy college students and young professionals, not necessarily fashionistas. I sell the truly designer stuff at Wasteland, another local store that focuses more on distinctive designer things.
Just for a sense of how the money works out - Crossroads gives 50% of their tag price in store credit or 30% in cash. Wasteland gives 35% in cash. Both are very picky but when Wasteland does buy things they price them pretty high. Crossroads would put a price tag of like $20 for a Madewell sweater; Wasteland might not buy that sweater but would price an Allsaints sweater at $50.
I have no idea how pricing works elsewhere or online.
Oh, and I tried a fussier, true consignment store once and almost none of my stuff sold after being in display for months. I decided consignment is less appealing than selling up front.
I have considered selling on Poshmark but the effort of individually selling things is off putting. I think they make shipping easy though. No way I'm doing eBay - I'm horrible about shipping things. I've also considered one of the ones where I mail a box in and they sort through and take things. I might do that for The Real Real (very designer) but otherwise I'll stick to my local brick & mortar places. But it does take a lot of time to go sell things to stores in person (there's always a line).
Finally, there are a few smaller online venues. There was an instagram group where I sold a few trendy things and kept the whole selling price. And I came across the blog Grechen's Closet (via YLF) that has its own resale site for "slow fashion". (Everlane is a brand they like to sell for sure.) Finally, there's the off-topic Style Exchange thread here at YLF but that's less focused on making money and more on finding things a new home for a small price. (But hey if any of your Everlane stuff is black and XS let me know. )
Trying to sell can be exhausting and demoralizing. Crossroads used to reject almost all my clothes, but as my own clothing budget increased and as I learned what they like, my success rate went up a lot. Before I sell, I go through and de-cat-hair everything and even steam or iron things that are high value but wrinkled. I fold things neatly and keep them in boxes until enough piles up to go sell.
